[M3_Dylan_]

I’m debating between going catless downpipes or catless midpipes on my M2, but I have a few questions. My M2 is my daily, and I already have one loud car, so I don’t want anything too in-your-face.

I know the DP's will produce more power since they’re removing restrictions closer to the turbo, but how much more power are we talking compared to midpipes? The midpipes seem really restrictive with that big elbow, and secondary cats + the easier install is a bonus. If the power difference is only 15-20 HP, it’s probably not worth it for me, but if it’s more like 30+ HP, then I might consider going with the downpipes or eventually both

Anyone here running catless setups on their M2? I’d love to hear your experiences with power gains, sound differences, and daily drivability.

Thanks!

[curtdragon]

Midpipes aren’t really removed for power. It’s mostly for sound. Downpipes definitely add power but more sound which is usually raspy. Also can trigger CEL.

Unless you’re tuning the car you don’t really need to change the dp. However even then you don’t need to unless you’re doing a “stage 2” upgrade

[priitserk]

I removed my catless downpipes.

I ordered MAD US single non resonated midpipe and catless downpipes and OEM axelback.

When valves open, its effectively straight through system and it was so loud that I would be instantly banned from any track and police would probably stop me quickly in the city. Used dB meter and it recorded 108dB at 3000 rpm. More than 120dB when going hard.

Even with valves closed it was painfully loud, was around 10-12dB quieter but still exceeds any noise limits in city and in any track in Europe.

Turbo spool was fast.

Also had lot of installation issues as the quality is not the best one.
I dont recommend that setup. It's really too loud.

[M3_Dylan_]

Originally Posted by curtdragon

Midpipes aren’t really removed for power. It’s mostly for sound. Downpipes definitely add power but more sound which is usually raspy. Also can trigger CEL.

Unless you’re tuning the car you don’t really need to change the dp. However even then you don’t need to unless you’re doing a “stage 2” upgrade

I was thinking a similar thing. Most of my cars I had/have custom DPs and midpipes but on my last daily I tossed some basic catless midpipes on for sound. I was suprised my tuner told me I was only missing out on 20ish awhp by keeping the stock DPs so I did. Not sure if it was a similar situation for the S58. I know everyone says “down pipes and tune” but with new cars i’m starting to question how much restriction & noise reduction manufactures are pushing back to the midpipes off the DPs.

Also, thanks for reminding me about the CEL! I forgot that I have to send my ECU half-way across the world to code then out 😂. I might do catted midpipes now and then catless DPs when I unlock it that way I can have sound now but not too much sound once I go catless DPs down the road if that makes sense???

[curtdragon]

For the B58 absolutely get a downpipe and a tune. They sound so much better even with the downpipe but for the S58 they don’t sound too good and they’re super loud when you add a downpipe it’s very hard to get it to sound really nice. A mid pipe will add some some power but I think if you add a tune you’ll be satisfied and it’s not absolutely necessary to get a downpipe unless you’re chasing numbers. Also, you have to consider the smell. I’m sure you already know you said you had other cars with downpipe so if you get a catless one it’s going to be loud and smelly.

[Ehloo]

its all about flow with turbo engines. the quicker the air can get in and out will yield power gains. i would argue the midpipe should yield some power gains as you are removing the extra cats but the down pipe is the real restriction coming right off the turbo.

but there is pro and cons to carless downpipes. the smell is pretty bad and actually really bad for you. when you sit at stop lights you better close your windows as you will smell it and also when it lingers in your garage.

the middle ground is highflow catted downpipes. reduces smells and still yields good power gains

[M3_Dylan_]

Originally Posted by priitserk

I removed my catless downpipes.

I ordered MAD US single non resonated midpipe and catless downpipes and OEM axelback.

When valves open, its effectively straight through system and it was so loud that I would be instantly banned from any track and police would probably stop me quickly in the city. Used dB meter and it recorded 108dB at 3000 rpm. More than 120dB when going hard.

Even with valves closed it was painfully loud, was around 10-12dB quieter but still exceeds any noise limits in city and in any track in Europe.

Turbo spool was fast.

Also had lot of installation issues as the quality is not the best one.
I dont recommend that setup. It's really too loud.

Thanks for sharing your experience! With dB read outs too wow! From my research, it seems like the consensus is a single midpipe is what makes the S58 sound the best - and also cheaper than equal length dual pipes. I dont have any sound laws where I live in States but 120dB is pushing it for an everyday car living in the city. Maybe resonated midpipes with some quality catless DPs? Or keep everything OEM besides catless DPs and bite the bullet on having a stock exhaust until the ECU is unlocked?

[mike@x-ph.com]

If your goal is sound, start with the single resonated midpipe. It significantly improves the sound without adding any unwanted noise.

If you want more sound after, you can get catted downpipes and/or axle back

If your goal is sound and power, the downpipes are the way to go.

I would skip Catless as it's too raspy, in my opinion, and will produce a foul smell.

[M3_Dylan_]

Originally Posted by Ehloo

its all about flow with turbo engines. the quicker the air can get in and out will yield power gains. i would argue the midpipe should yield some power gains as you are removing the extra cats but the down pipe is the real restriction coming right off the turbo.

but there is pro and cons to carless downpipes. the smell is pretty bad and actually really bad for you. when you sit at stop lights you better close your windows as you will smell it and also when it lingers in your garage.

the middle ground is highflow catted downpipes. reduces smells and still yields good power gains

Oh yeah, the amount of fumes I have inhaled from my younger years driving a catless E46 M3 all the time for sure took some time off my life. I also showed up to everything smelling slightly like exhaust. Back then I thoughg it was cool - like yeah I drive around in a sports car intended for the track everyday because i’m a “real” enthusiast 😂. But yeah those days are over… With a highflow catted DP do they usually come with C02 bungs to avoid a CEL? Thanks!

[techwhiz1]

I like power, but I also believe in a.clean environment.

Going with an M2 means you already compromised on Max power from a S58.

That being said, I'm not an advocate of removing the catted downpipes. Go for the rest.

Catless DP stink. Plain and simple.

[M3_Dylan_]

Originally Posted by mike@x-ph.com

If your goal is sound, start with the single resonated midpipe. It significantly improves the sound without adding any unwanted noise.

If you want more sound after, you can get catted downpipes and/or axle back

If your goal is sound and power, the downpipes are the way to go.

I would skip Catless as it's too raspy, in my opinion, and will produce a foul smell.

Can you run high-flow catted downpipes without a CEL? I know I won't see any power gains until the car is tuned, but I would like to wake up the exhaust a bit now and then in the future take advantage of the higher flow once the car is tuned. Thanks!

[jmg]

This video shows +20hp on just a single midpipe, which is crazy! Is this legit? Same day same dyno.

[mike@x-ph.com]

Originally Posted by M3_Dylan_

Can you run high-flow catted downpipes without a CEL? I know I won't see any power gains until the car is tuned, but I would like to wake up the exhaust a bit now and then in the future take advantage of the higher flow once the car is tuned. Thanks!

you can run the active autowerke, milltek or fabspeed downpipes without the CEL.

the other less expensive brands will trigger the check engine light

[Bumpinjeep]

Originally Posted by jmg

This video shows +20hp on just a single midpipe, which is crazy! Is this legit? Same day same dyno.

I dont know, I feel a difference with the J Pipe and Mid pipe from ER. Is it 20 hp? Which is what a 4% difference? Without taking them off and dynoing and putting them back on and dynoing, there's really no way to know. However, I feel like the car is in boost easier, the throttle is more responsive, and it certainly does get squirlier under throttle. This may be because I have lighter wheels, intakes, and the exhaust, but I feel like there is a measurable difference before and after mods.
The biggest and by far and away the best thing here is the sound. To my ears, it is perfect.